The torque coefficient K (also referred to herein as the “K factor”) is a representation of the friction characteristics of threaded part surfaces. These friction characteristics are a design assumption that relates to the expected clamp load achieved with an applied torque.
The torque coefficient K is calculated using the equation:K=T/(D×W)where:
K=Torque Coefficient (unitless),
T=Torque applied to the test piece (Nm),
D=Nominal Thread Diameter of the threaded component being tested (mm), and
W=Axial load created at the applied Torque value (kN).
The K factor is typically calculated by applying a known torque and measuring the axial load produced from the applied torque. A conventional technique used to measure the axial load created by the applied torque includes using a donut-shaped load washer that is compressed by the applied torque. The threaded component to be measured—such as a bolt extends through a flat washer, a holding fixture, the instrumented load washer, a second flat washer, and finally a nut. With an assembly in this series, the threaded component to be measured must be a minimum of three inches in length.
Many hydraulic fittings and couplings are less than one inch in length. The axial load created by torque applied to these fittings cannot be directly measured using such a conventional technique, and, thus, the torque coefficient for production parts cannot be defined. Instead, the torque coefficient is inferred by measuring surrogate sample bolts which are plated with the fittings in place of the actual component ultimately used in production.
Chinese Utility Model No. CN 200947081 Y is entitled, “Portable Digital Display Torque Coefficient Tester.” The utility model claims a portable digital display torque coefficient tester convenient for use in spot testing the torque coefficient. The tester includes a bracket, an axial force sensor that is fixedly set in the bracket, and a clamping shaft force-transfer mould that is connected to the axial force sensor. One end of the axial force sensor is connected to the clamping shaft force-transfer mould. The other end of the axial force sensor is connected to the bracket. The axial force sensor is connected to a handset meter through a data wire. A torque sensor is connected to the handset meter through a data wire. The tester can directly test the torque coefficient at a job location or on a work piece to harmonize the actual shaft force of the bolt with the designed and requiring shaft force and can directly test the fastening torque value under designed shaft force.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some regards and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.